Line data Source code
1 : /*
2 : * Copyright (c) 2012 The WebRTC project authors. All Rights Reserved.
3 : *
4 : * Use of this source code is governed by a BSD-style license
5 : * that can be found in the LICENSE file in the root of the source
6 : * tree. An additional intellectual property rights grant can be found
7 : * in the file PATENTS. All contributing project authors may
8 : * be found in the AUTHORS file in the root of the source tree.
9 : */
10 :
11 : #include "webrtc/system_wrappers/include/rtp_to_ntp_estimator.h"
12 :
13 : #include "webrtc/base/logging.h"
14 : #include "webrtc/system_wrappers/include/clock.h"
15 :
16 : namespace webrtc {
17 : namespace {
18 : // Number of RTCP SR reports to use to map between RTP and NTP.
19 : const size_t kNumRtcpReportsToUse = 2;
20 :
21 : // Calculates the RTP timestamp frequency from two pairs of NTP/RTP timestamps.
22 0 : bool CalculateFrequency(int64_t ntp_ms1,
23 : uint32_t rtp_timestamp1,
24 : int64_t ntp_ms2,
25 : uint32_t rtp_timestamp2,
26 : double* frequency_khz) {
27 0 : if (ntp_ms1 <= ntp_ms2)
28 0 : return false;
29 :
30 0 : *frequency_khz = static_cast<double>(rtp_timestamp1 - rtp_timestamp2) /
31 0 : static_cast<double>(ntp_ms1 - ntp_ms2);
32 0 : return true;
33 : }
34 :
35 : // Detects if there has been a wraparound between |old_timestamp| and
36 : // |new_timestamp|, and compensates by adding 2^32 if that is the case.
37 0 : bool CompensateForWrapAround(uint32_t new_timestamp,
38 : uint32_t old_timestamp,
39 : int64_t* compensated_timestamp) {
40 0 : int64_t wraps = CheckForWrapArounds(new_timestamp, old_timestamp);
41 0 : if (wraps < 0) {
42 : // Reordering, don't use this packet.
43 0 : return false;
44 : }
45 0 : *compensated_timestamp = new_timestamp + (wraps << 32);
46 0 : return true;
47 : }
48 :
49 0 : bool Contains(const std::list<RtpToNtpEstimator::RtcpMeasurement>& measurements,
50 : const RtpToNtpEstimator::RtcpMeasurement& other) {
51 0 : for (const auto& measurement : measurements) {
52 0 : if (measurement.IsEqual(other))
53 0 : return true;
54 : }
55 0 : return false;
56 : }
57 :
58 0 : bool IsValid(const std::list<RtpToNtpEstimator::RtcpMeasurement>& measurements,
59 : const RtpToNtpEstimator::RtcpMeasurement& other) {
60 0 : if (!other.ntp_time.Valid())
61 0 : return false;
62 :
63 0 : int64_t ntp_ms_new = other.ntp_time.ToMs();
64 0 : for (const auto& measurement : measurements) {
65 0 : if (ntp_ms_new <= measurement.ntp_time.ToMs()) {
66 : // Old report.
67 0 : return false;
68 : }
69 0 : int64_t timestamp_new = other.rtp_timestamp;
70 0 : if (!CompensateForWrapAround(timestamp_new, measurement.rtp_timestamp,
71 : ×tamp_new)) {
72 0 : return false;
73 : }
74 0 : if (timestamp_new <= measurement.rtp_timestamp) {
75 0 : LOG(LS_WARNING) << "Newer RTCP SR report with older RTP timestamp.";
76 0 : return false;
77 : }
78 : }
79 0 : return true;
80 : }
81 : } // namespace
82 :
83 0 : RtpToNtpEstimator::RtcpMeasurement::RtcpMeasurement(uint32_t ntp_secs,
84 : uint32_t ntp_frac,
85 0 : uint32_t timestamp)
86 0 : : ntp_time(ntp_secs, ntp_frac), rtp_timestamp(timestamp) {}
87 :
88 0 : bool RtpToNtpEstimator::RtcpMeasurement::IsEqual(
89 : const RtcpMeasurement& other) const {
90 : // Use || since two equal timestamps will result in zero frequency and in
91 : // RtpToNtpMs, |rtp_timestamp_ms| is estimated by dividing by the frequency.
92 0 : return (ntp_time == other.ntp_time) || (rtp_timestamp == other.rtp_timestamp);
93 : }
94 :
95 : // Class for converting an RTP timestamp to the NTP domain.
96 0 : RtpToNtpEstimator::RtpToNtpEstimator() {}
97 0 : RtpToNtpEstimator::~RtpToNtpEstimator() {}
98 :
99 0 : void RtpToNtpEstimator::UpdateParameters() {
100 0 : if (measurements_.size() != kNumRtcpReportsToUse)
101 0 : return;
102 :
103 0 : int64_t timestamp_new = measurements_.front().rtp_timestamp;
104 0 : int64_t timestamp_old = measurements_.back().rtp_timestamp;
105 0 : if (!CompensateForWrapAround(timestamp_new, timestamp_old, ×tamp_new))
106 0 : return;
107 :
108 0 : int64_t ntp_ms_new = measurements_.front().ntp_time.ToMs();
109 0 : int64_t ntp_ms_old = measurements_.back().ntp_time.ToMs();
110 :
111 0 : if (!CalculateFrequency(ntp_ms_new, timestamp_new, ntp_ms_old, timestamp_old,
112 : ¶ms_.frequency_khz)) {
113 0 : return;
114 : }
115 0 : params_.offset_ms = timestamp_new - params_.frequency_khz * ntp_ms_new;
116 0 : params_.calculated = true;
117 : }
118 :
119 0 : bool RtpToNtpEstimator::UpdateMeasurements(uint32_t ntp_secs,
120 : uint32_t ntp_frac,
121 : uint32_t rtp_timestamp,
122 : bool* new_rtcp_sr) {
123 0 : *new_rtcp_sr = false;
124 :
125 0 : RtcpMeasurement measurement(ntp_secs, ntp_frac, rtp_timestamp);
126 0 : if (Contains(measurements_, measurement)) {
127 : // RTCP SR report already added.
128 0 : return true;
129 : }
130 0 : if (!IsValid(measurements_, measurement)) {
131 : // Old report or invalid parameters.
132 0 : return false;
133 : }
134 :
135 : // Insert new RTCP SR report.
136 0 : if (measurements_.size() == kNumRtcpReportsToUse)
137 0 : measurements_.pop_back();
138 :
139 0 : measurements_.push_front(measurement);
140 0 : *new_rtcp_sr = true;
141 :
142 : // List updated, calculate new parameters.
143 0 : UpdateParameters();
144 0 : return true;
145 : }
146 :
147 0 : bool RtpToNtpEstimator::Estimate(int64_t rtp_timestamp,
148 : int64_t* rtp_timestamp_ms) const {
149 0 : if (!params_.calculated || measurements_.empty())
150 0 : return false;
151 :
152 0 : uint32_t rtp_timestamp_old = measurements_.back().rtp_timestamp;
153 : int64_t rtp_timestamp_unwrapped;
154 0 : if (!CompensateForWrapAround(rtp_timestamp, rtp_timestamp_old,
155 : &rtp_timestamp_unwrapped)) {
156 0 : return false;
157 : }
158 :
159 : double rtp_ms =
160 0 : (static_cast<double>(rtp_timestamp_unwrapped) - params_.offset_ms) /
161 0 : params_.frequency_khz +
162 0 : 0.5f;
163 :
164 0 : if (rtp_ms < 0)
165 0 : return false;
166 :
167 0 : *rtp_timestamp_ms = rtp_ms;
168 0 : return true;
169 : }
170 :
171 0 : int CheckForWrapArounds(uint32_t new_timestamp, uint32_t old_timestamp) {
172 0 : if (new_timestamp < old_timestamp) {
173 : // This difference should be less than -2^31 if we have had a wrap around
174 : // (e.g. |new_timestamp| = 1, |rtcp_rtp_timestamp| = 2^32 - 1). Since it is
175 : // cast to a int32_t, it should be positive.
176 0 : if (static_cast<int32_t>(new_timestamp - old_timestamp) > 0) {
177 : // Forward wrap around.
178 0 : return 1;
179 : }
180 0 : } else if (static_cast<int32_t>(old_timestamp - new_timestamp) > 0) {
181 : // This difference should be less than -2^31 if we have had a backward wrap
182 : // around. Since it is cast to a int32_t, it should be positive.
183 0 : return -1;
184 : }
185 0 : return 0;
186 : }
187 :
188 : } // namespace webrtc
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